利用信号量进行多线程通讯 首先在主程序中建立两个线程，然后设置信号量，每个线程循环等待符合要求的信号量，只要满足条件，则线程执行。该例为多线程通讯的简单实例，只是展示了原理-Signal was carried out using multi-threaded communication first in the main program to create two threads, and then set the semaphore for each thread to wait for